In conventional IC memory cards operating in conformity with the PCMCIA memory card specification, as shown in FIG. 7, only accesses to a common memory circuit 76 and a card attribute memory circuit 74 located at even-numbered addresses of an attribute memory region 73 which stores an attribute of the IC memory card are made effective, and the IC memory card operates by exchanging effective data. An external system 78 is allowed to access the common memory circuit 76 and the card attribute memory circuit 74 via a connector 71, an interface circuit 72 and an even attribute control circuit 77, but an access to an odd attribute region 75 is made disable and there is provided no function accessible to this region.
However, with the above arrangement, when a function other than the data storage function is to be performed by sending data other than preservative data such as special data or commands to the IC memory card, no distinction can be made between the preservative data and the special data because of an obstacle that only transmission and reception of the data conformable to the specification are effective, and therefore there arises a problem that it is difficult to transmit and receive the special data without affecting the inherent functions.